Before taxi.
Flaps ............................................................ .............................. Check
Move the flaps from Flaps Up to Flaps 40 back to Flaps up (i.e., full travel) to ensure freedom of movement.
If remote de-icing is planned or if the taxi route is through slush or standing water in freezing conditions, or if precipitation is falling in freezing conditions, taxi out with the flaps up. Taxiing with the flaps extended subjects the flaps and flap drives to contamination. Leading edge devices are also susceptible to slush accumulations.
This always gave me trouble. My limited common sense wanted to adjust this; but had some resistance from F/O's & LTC's. The above statement is what was on my checklist. It was snowing at the gate, but de-icing was quite a distance from the apron; thus we needed to taxi a long way before being sprayed. I suggested we taxi out with flaps up and after de-icing do the F40 exercise thingy. Oh no. It was met with horror. I surmised that to open the flaps in snow, and then close then again, could trap snow in the gaps which would be compressed and not be influenced by the de-icing fluid. It was insisted that we exercise the flaps before taxi, de-ice and then taxi with flaps up to the holding point.
Opinions please. Am I mad, or what?